Alumina ceramics are widely used for their general sturdiness and good conductivity of heat. Compared with similar materials, such as aluminum nitride ceramics, alumina ceramics are very cost effective. The manufacturing and material costs of alumina ceramics are relatively inexpensive and provide high yields of the items manufactured.
Prior to this invention, however, alumina ceramics could not be used in high thermal stress applications. Such applications involve one part of the ceramic being at substantially different temperature than another part. In a toner fuser, high stress occurs when a narrow thick media is being fused in a heater wide enough for standard media. The ceramic cracks because the media cools the region of the ceramic to which it is proximate, while the more distant parts of the ceramic are spaced both from the media and a backup support surface and gain temperature. In a stovetop-cooking environment, such thermal stress would occur when relatively cool water is spilled on part of the burner.
Overcoming this thermal stress weakness of alumina ceramics permits this cost effective material to be used in a wide variety of applications where it could not previously have been used. During the manufacturing process, alumina ceramics can be shaped, for example, in the form of a pot, and subsequently fixed in that form. Therefore, the usefulness of overcoming thermal stress in alumina ceramics is not limited to applications having flat surfaces.
This invention employs a described alumina ceramic laminate. Laminate ceramic printing elements having printed dots of heating elements, typically of size of 0.125 mm in diameter, is known. Since the heating elements are individual elements, the heating area of each heating element is small relative to the surface area of the ceramic support. A preferred alumina ceramic laminate employed with this invention is obtained from Nikko Company, of Japan, under their product designation, 500-459. However, other ceramic laminate materials having the characteristics of the alumina ceramic laminate may also be used.